Ever since the concept of paid-for data access has been first implemented, content providers have had to work a delicate balance between inconveniencing legitimate users by excessive access constraints and implementing a sufficient number of protective techniques to stop or at least to slow down the ever more creative data pirates.
For example, one of the major inconveniences of a traditional video rental model is the necessity to return a rented video or a videogame to the rental outlet on time. By demanding a timely return of the rentals, the content providers ensure that the duration of the rental period is properly enforced (creating a major hassle for their customers in the process). To mitigate the inconvenience resulting from the necessity to return rented tapes and DVDs, a rent-by-mail service is currently offered by Netflix Inc. and WalMart Inc., where a client pays a monthly fee for the right to hold several video DVDs. When some of the DVDs are mailed back to a warehouse, new rentals can be ordered. GameFly Inc. and GamesForRent Inc. offer similar rent-by-mail service for videogames. Even though the rent-by-mail model has advantages over the traditional rental model, it still requires customers to return rented material, increasing the overall costs and creating the blackout periods during DVDs shipping time.
While shipping costs have been steadily growing over the years, the prices of digital storage media, such as DVD-R disks, have been falling. Eventually it will be more economical to discard the data storage medium after the expiration of the data rental period than to return the used data storage medium to the data provider. There is, however, a necessity to come up with a method and a system which would allow data providers to enforce the terms of the rental agreements without reclaiming the rented data storage media. A well researched way of data distribution involves a dedicated set-top box which electronically receives encoded data from a central location, stores a large read-only library of data, or reads data from freely distributed data media, such as CDs or DVDs. When a subscriber selects a data file for usage, the set-top box contacts the central computer to request the decoding key or to process a billing request. In order to mass-customize the production of optical disks, a unique code may be formed on an optical disk mass-molded from a master substrate by removing the reflective coating from selected portions of the information recording area to form a code pattern. The sophistication of the processing set-top device and the general complexity of this method render it practically unusable.
One way to slow down the piracy, discussed in a number of US patents, is to encode data on perishable media. A typical perishable medium would have a reactive compound which changes from an optically transparent state to an optically opaque state when subjected to readout light and/or atmospheric oxygen, or decays after a certain pre-determined time interval. In the alternative embodiment, an unstable compound temporarily flattens the textured surface and enables the optical readout of the data. With time the optical transmission through the surface is reduced, as the unstable compound is gradually removed via sublimation and the texture of the surface is revealed. In another variation, a light-changeable compound is incorporated into a section of an optical medium. The compound temporarily distorts the digital data output from a section of the recording layer. As most optical media players are pre-programmed to re-sample data areas of the recording layer to assure correct copying, the varying output from the disclosed optical medium prevents copying. The more exotic alternative includes a breakable reservoir with chemical agent that interacts with the data storage portion to render it unreadable after a specified period of time. The concept of perishable data medium, while attractive in principle, suffers from several drawbacks. In many cases the manufacturing process has to take place in the oxygen-free atmosphere, increasing costs. The timing of the decay may vary depending on the surrounding conditions. For example, while the medium may be designed to decay within a certain number of days at room temperature, it may decay much slower at lower temperatures. A street smart user could simply keep his movie library in a freezer, circumventing the intended data usage agreement. Alternatively, the media designed to decay in laboratory conditions from exposure to oxygen may stay virtually decay free if intentionally covered with a microscopic layer of machine oil which would prevent atmospheric oxygen from reaching its intended target.
With the advances in home computer technology, an average consumer having an average PC will soon be able to make an exact replica of a rented or purchased DVD, containing a video, videogame or any other video content. As such technology becomes widely available, the current video distribution model no longer protects the content providers from data piracy. A similar problem is already evident in the case of the music industry: an audio CD can no longer be safely rented (or even sold), since it offers virtually no protection against illegal copying. In a remarkable show of desperation, the Recording Industry Association of America disclosed a method and system of marking data media products by introducing a tracing substance into a polycarbonate or polystyrene composition during the manufacturing stages of CDs or DVDs a technique commonly reserved for tracking explosives by Government anti-terrorist agencies. Therefore, there is a pressing need for new ways to enforce the copyright protection of data.